A growing number of public schools have adopted reforms that increase the amount of time students spend in school. However, the potential costs of such reforms are not well understood. In this article, we report findings from a resource-cost study conducted in four schools that participated in the Massachusetts Expanded Learning Time Initiative. We find large differences in per-pupil costs among schools. Cost differences were associated with how schools used and staffed the additional time. Findings raise questions about the cost feasibility of expanded time reforms in public schools based on existing federal, state, and private funding initiatives.